Grid electrode for electron discharge devices



Jan. 6, 1953 c, FOULKES 7 2,624,100

GRID ELECTRODE FOR ELECTRON DISCHARGE DEVICE Filed Jan. 18, 1.945

Invenlor Patented Jan. 6, 1953 GRID ELECTRODE FOR. ELECTRON DISCHARGE DEVICES Christopher Henryj'Eoulkes, London, England, as;-

srgnor; by mesneiassignments, to International Standard Electric Corporation,

New York, N. Y.,

a. .corp oration of Delaware.

Application January 18, 1945; Serial No.- 573,459 In Great Britain November 2, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires Novemberz, 1963.

1 Claim.

The present invention relates to improvements in the manufacture of grid electrodes for elec-v tron discharge devices, and in particular for devices of the kind in which the grid substantially comprises a grated window in a metal disc sealed through the envelope of the device.

The usual practice hitherto adopted for making a grid of this kind is as follows:

A stout backing plate with a suitable opening is evenly wound with fine wire across the opening, successive turns being suitably spaced apart. The wound plate is plated with copper or gold and is then heated until the copper or gold fuses thus attaching the wires to the plate. The wires on the back of the plate are then removed, and the complete grid structure is soldered with tin to the metal disc, which is subsequently sealed through the envelope of the device and serves as the terminal for the grid.

In order that the grid wires should remain straight and even during this process, the wire and backing plate must have the same co-eflicient of expansion. This presents no difficulty when pure metals are used, but with alloys the composition cannot be accurately repeated with different batches, and as a result the co-efficient of expansion is variable in an unpredictable manner.

It has been the practice hitherto to use pure molybdenum or tungsten as the material for the wire and backing plate of the grid. It is found, however, that very fine molybdenum or tungsten wires, say less than 0.0005 in diameter, are not easily obtainable in long lengths. For this reason other materials have had to be employed, and of these stainless steel has been found the most suitable. It can be satisfactorily drawn down into very fine wire, it is tough and easily handled, and resists corrosion.

The principal object of the present invention, therefore, is to provide a design and manufacturing process for grids of the kind described which do not require the use of an accurately controlled co-efiicient of expansion of the material used.

The invention, therefore, consists in a method of making a grid for an electron discharge device which comprises winding with wire a bent sheet of springy material so as to overlap an opening in the sheet provided with raised resilient supporting means for the wire at the edges of the opening, attaching each turn of the wire to the supporting means at both sides of the opening, removing the excess wire, and flattening out the sheet.

The invention also provides a grid for an elec tron discharge device comprising a supporting plate of springy material having an aperture therein, raised resilient support means attached to or formed on the plate in the neighbourhood of the edges of the aperture, and a plurality of parallel wires attached at both ends to the said supporting means, all of the said wires being in a state of tension when the supporting plate is The invention will be described with reference to the accompanying drawing in which:

Fig. 1 shows a grid according to the invention; and

Fig. 2 shows a stage in the process of making the grid.

Fig. 1 shows a thin supporting plate I of thin springy material such as beryllium copper (for example 0.005 thick) having therein a rectangular opening 2, two parallel sides of which are bent upwards, and curved over as shown at 3 and 4 to form the ultimate resilient supporting bridges for the grid wires 5. Referring now to Fig. 2 the supporting plate I is bent into a small arc in the manner indicated, and is evenly wound with appropriate wire 5, the bending being such that the turns of wire just make contact with the bridges 3 and 4. The wires are then soldered to the bridges with silver solder and the excess wire not required is removed. The supporting plate I is then flattened out, thus stretching the wires 5 taut and flexing slightly at the same time the supporting bridges 3 and 4. The wires then remain straight, and the effect of any difference between the coefi"1cients of expansion of the wire and the supporting plate is taken up by the resilience of the bridges. It will be understood that the opening in the plate I could be other than rectangular in shape, and the wires could be supported on any suitable resilient support means or bridges formed or punched out of, or fixed .to, the plate on either side of the opening.

When the supporting plate is very thin, it is preferable to attach it by welding to a stout backing plate 6 (Fig. 1), provided with a central opening registering with the grid. This will ensure that it is kept flat. The grid assembly (with or without the backing plate) may then be attached to the disc terminal by soldering or welding.

In U. S. Patent No. 2,282,392, issued May 12, 1942, there is described a special type of grid of disc form designed to remain fiat in spite of temperature changes. The wires of this grid are 3 formed into a particular shape, and different coefiicients of expansion of the materials of the wires and support are necessary. In the case of the present invention the wires do not have to be specially formed, nor is any requirement imposed for co-efiicient of expansion.

What is claimed is:

A method of making a grid for an electron dis- 0 7 charge device which comprises cutting an opening in a sheet of springy material, bending up two opposite edges of the opening to form resilient supporting bridges, bending the sheet into a small arc about an axis parallel to the bridges, winding wire evenly round the sheet over the bridges, attaching each turn of wire to each of the bridges, removing the excess wire, and flattening out the sheet.

CHRISTOPHER HENRY FOULKES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'I 'ENTS Number Name Date 1,106,516 Lachman Aug. 11, 1914 1,472,505 Trimble Oct. 30, 1923 1,822,370 Perry Sept. 8, 1931 2,048,225 Snow July 21, 1936 2,054,119 Daene Sept. 15, 1936 2,282,392 Bieling May 12, 1942 2,386,018 Watter Oct. 2, 1945 OTHER REFERENCES Book entitled 369 Job Pointers, page 83. 

